1. Field of the Invention
The present invention relates to a magnetic tape cassette and, in more particular, to a magnetic tape cassette in which a pair of tape reels for a magnetic tape to be wound therebetween and thereround and a pair of engaging members are improved.
2. Related Art
As known well, in a video unit such as a VTR and the like, there is often used a magnetic tape cassette including a pair of tape reels contained in a cassette case. The pair of tape reels each includes upper and lower flanges disposed on the upper and lower side surfaces of a reel hub which is a winding core barrel part. Formerly, for example, there was employed a structure in which lower flanges and a reel hub were formed integrally with each other while upper flanges were bonded to, welded to, or fitted with the other end side of the reel hub.
However, when the tape cassette has a structure in which the tape reel is to be assembled in the above manner, then the number of parts and the number of steps of operation are both increased and, therefore, there has been proposed such a tape reel 1 as shown in FIG. 5. That is, in the illustrated tape reel 1, a reel hub 2, lower flanges 3 and upper flanges 4 are formed integrally together.
The tape reels 1 are disposed side by side in a rotatable manner in upper and lower cassette halves (which are not shown) and a magnetic tape (not shown) is extended between and over the respective tape reels 1. Further, engaging gears 5 are formed on the outer peripheral portions of the lower flanges 3 and, in the neighborhood of the engaging gears, there are provided a pair of brake claws 11 which are used to stop the rotational movements of the tape reels 1.
The two brake claws 11 are disposed at right and left symmetrical positions with the right-and-left direction central line of the cassette case between them, and are also freely oscillatable along the bottom surface of the cassette. Each of the brake claws 11 includes a cylindrical rotary barrel portion 12, and a claw portion 13 and a moving portion 14 respectively formed integrally with the rotary barrel portion 12.
The rotary barrel portion 12 is inserted over a shaft 15 provided integrally with the lower cassette half and is supported in a freely rotatable manner. Also, a spring 16 is inserted through the shaft 15. One end of the spring 16 is secured to one end of the claw portion 13, while the other end thereof is secured to a fulcrum shaft 17 formed integrally with the lower cassette half. Further, although not shown, as known well, between the two brake claws 11 there is incorporated a pressure member which can be oscillated along a plane perpendicular to the bottom surface of the cassette to press against the moving portion 14. When the cassette is loaded into a recording and reproducing device, the pressure member is pushed up and rotated by a lever or the like which comes in from the device.
While the cassette is not in use, the claw portion 13 is energized by the spring 16 into engagement with the engaging gear 5, whereby the two tape reels 1 are prevented from rotating. On the other hand, if the cassette case is loaded into the recording and reproducing device, then the moving portion 14 is pushed in a direction of an arrow A by the pressure member to remove the engagement between the claw portion 13 and engaging gear 5 against the energizing force of the spring 16, thereby allowing the two tape reels 1 to be rotated.
Next, referring to the manufacture of the tape reel 1, the tape reel 1 is integrally molded by such a metal mold 61 as shown in FIG. 6. That is, the tape reel 1 is molded by injecting resin into an injection space formed between an upper metal mold 7 and a lower metal mold 8 and, in order to form the upper flanges 4 integrally, there are provided projecting core portions 9 which are to be inserted through openings 6 formed in the lower flanges 3, respectively.
In order to form the engaging gear 5 in the lower flanges 3, the outer peripheral portions of the lower flanges 3 must be continuous and, for this reason, the diameter of the upper flange 4 cannot help but be smaller than the diameter of the lower flange 3. Also, in the core portion 9, there is provided a removing slope which facilitates the removal of the upper and lower metal molds 7, 8. Even according to this structure, the diameter of the upper flange 4 is smaller than the diameter of the lower flange 3, as can be seen clearly from FIGS. 5 and 6.
In the above-mentioned structure that there is a difference between the diameters of the upper and lower flanges 3 and 4, for example, if a magnetic tape is wound full to the lower flange 3 having a larger diameter, then the magnetic tape is forced out. In this case, the winding of the magnetic tape gets out of shape, which unfavorably provides a cause to damage the tape. This limits the quantity of winding of the magnetic tape to be wound round the tape reel 1.
However, when the removing slope of the metal mold and the strength of the lower flange 3 are taken into consideration, then there is a limit to increasing the diameter of the upper flange 4. If the diameter of the upper flange 4 is daringly increased, then the opening 6 is expanded accordingly, which decreases the thickness of the outer peripheral portion of the lower flange 3. As a result, when the claw portion 13 is engaged with the engaging gear 5, there is increased the possibility that the forming position of the opening 6 can be broken and thus the reliability of the tape reel can be impaired.
On the other hand, in Japanese Patent Publication No. Hei. 2-122486, there is disclosed a proposal to solve the above-mentioned problems, in which a projection is provided in part of the periphery of the upper flange 4. However, this proposal cannot solve the above problems radically and the problems are still left unsolved.